A typical automatic fire sprinkler has a body with an outlet that is normally closed by a plug, the plug being held in place by a heat-activated trigger mechanism, and an orifice normally just upstream of the outlet. Automatic sprinklers of the pendent type also have a substantially horizontal water distribution deflector facing the outlet. When a sufficiently elevated temperature is sensed, a thermally responsive element normally retaining the plug in a closed position releases the plug, allowing a vertically directed stream of water (downward for pendent sprinklers and upward for upright sprinklers) to rush from the outlet orifice towards the deflector. The water, impacting on the deflector, is diverted generally radially downward and outward, breaking into a spray pattern, the shape of which is, in large part, a function of the deflector configuration, projecting over the intended area of coverage, i.e. "the protected area".
Within the past three years, the range of available fire protection products for automatic fire sprinkler systems has expanded to include ceiling sprinklers designed to cover larger or "extended coverage" areas, when the occupancy being protected falls into the Ordinary Hazard category, as defined by NFPA 13, Standard for the Installation of Sprinkler Systems. These sprinklers are referred to as extended coverage/ordinary hazard (ECOH) sprinklers. In order to be acceptable for installation under an installation standard like NFPA 13, an automatic fire sprinkler must appear in a list published by an organization acceptable to the authority having jurisdiction, and meet any additional requirements specified in the installation standard. organizations listing ECOH sprinklers include, e.g., Underwriters Laboratories Inc. (ULI) and Factory Mutual Research Corporation (FMRC). These, and other, similar, organizations evaluate the performance of fire protection products, like ECOH sprinklers, in accordance with established standards or guidelines, to certify that the listed fire protection products will satisfactorily perform their intended function when installed in accordance with the requirements of their listing, the manufacturer's installation instructions, and the installation standards of the authority having jurisdiction.
The standards or guidelines for evaluating ECOH sprinklers include established requirements for the minimum amount of water which must be collected during testing per unit time and in specified areas (i.e., density) under and between the sprinklers when discharging water under specified flowing (residual pressure) conditions. The testing may be conducted both with and without the presence of fire.
ECOH pendent sprinklers developed thus far have utilized a series of relatively narrow slots located around the periphery of the deflector, in order to produce a spray pattern in which most of the water is directed radially outward to the outer portions of the larger (extended) area to be protected. This type of design, however, tends to yield a light area of spray with water droplets having low downward momentum within the inner portion of the pattern and beneath the sprinkler. If a fire starts beneath the sprinkler, the upward draft of the fire plume can overcome the downward momentum of water droplets being discharged beneath the sprinkler, if it is excessively light, thereby uplifting the spray pattern and resulting in a nil quantity of water penetrating to the seat of the fire to enable extinguishment.